$\left[\begin{array} {ccc} -4& -8\\ -1& 7\\ 1& 6\\ -9& 1 \end{array}\right]$ What are the dimensions of the matrix?
The first dimension is the number of rows in the matrix. There are $4$ rows. The second dimension is the number of columns in the matrix. There are $2$ columns. In conclusion, the dimensions of the matrix are $4\times 2$.